The present invention relates to a method and apparatus for disinfecting spaces such hospital rooms and the like.
The problem of micro-organism contamination of, for example, hospital bedrooms and the like has gown into an acute one in recent years and one particular method of disinfecting such spaces and any equipment located therein is the use of disinfecting sprays (atomisations) of liquid droplets such as hydrogen peroxide. These systems are often known as hydrogen peroxide fogging systems and such hydrogen peroxide fogging systems can involve vaporization of a low concentration hydrogen peroxide solution using a high frequency ultrasound (typically 1.6-2 MHz) droplet generator in an atomization chamber partially filled with solution. WO-A-2009-138430 discloses such a system and method designed to provide improved efficacy of such methods and which involves the steps of: (a) determining a first value of the relative humidity of the air in the space; (b) atomizing a disinfecting liquid in the space until a predetermined second value of the relative humidity of the air is reached in the space, and; (c) maintaining the relative humidity of the air for a predetermined time at the second value by means of atomizing the disinfecting liquid, wherein the method further comprises of decreasing the relative humidity of the air in the space prior to and/or during atomizing of the disinfecting liquid.
In such processes, under the influence of the ultrasonic droplet generator and through the mechanism of forced cavitation, small sized droplets (circa 1 μm diameter) are produced and ejected from the solution surface. Airflow from an electric fan then carries these droplets as a mist from the chamber via a venturi into the space to be treated. A combination of the fan's airflow and natural convection currents in the room carry these droplets until they contact surfaces where they are deposited and operate to destroy any organisms present. Given appropriate generating capacity for the space to be disinfected, if sufficient vaporised hydrogen peroxide is expelled from the system, statistically a good fog density and hence hydrogen peroxide distribution will be achieved in the space.
This traditional process is controlled via a closed loop system, with relative humidity (RH) being the controlling variable as described in WO-A-2009-138430. Tests have shown that in a closed environment (which is required for safety), RH increase is proportional to hydrogen peroxide concentration increase.
One of the primary factors affecting efficacy of the process is the profile of the airflow within the space being treated. Traditionally, with a regular electric fan operating in a closed space with no external ventilation (as required for safety), a reasonably static air distribution pattern is achieved which, depending on the layout of the room and its contents, can lead to areas of poor fogging coverage and hence droplet deposition, a phenomenon known as spatial differentiation and this in turn can lead to incomplete disinfection.